1. Field of the Invention
The present invention relates to a variable displacement compressor. More particularly, the present invention relates to a variable displacement compressor having a control valve for controlling the displacement of the compressor by controlling the pressure in the crank chamber.
2. Description of the Related Art
Vehicles typically have compressors employed in air conditioning systems. A compressor having a controllable refrigerant gas displacement is desirable for accurately controlling the interior air temperature to make the ride comfortable for the passengers. There is a type of compressor that is provided with a swash plate or a wobble plate tiltably supported on a rotary shaft. The inclination of the swash plate or the wobble plate is controlled based on the difference between the pressure in a crank chamber and the pressure in a suction chamber. The stroke of each piston is varied by the inclination of the swash plate.
Japanese Unexamined Patent Publication 2-115578 discloses such a compressor. As shown in FIG. 10, this compressor has a wobble plate 101 mounted on a rotary shaft 102 in a crank chamber 100. The wobble plate 101 is rotatable and tiltable with respect to the shaft 102. Pistons 104 are coupled to the wobble plate 101 by a rod 103. Rotation of the shaft 102 swings the plate 101 and reciprocates each pistons 104 in an associated cylinder bore 105 at a stroke corresponding to the inclination angle of the plate 101. The reciprocation of each piston 104 draws refrigerant gas into the cylinder bores 105 from the suction chamber 106. The refrigerant gas is then compressed in each cylinder bore 105 and discharged into the discharge chamber 107.
The crank chamber 100 is communicated with a chamber 110 via passages 108 and 109. An electromagnetic control valve 111 is provided in a rear housing 112 of the compressor. The inlet port of the control valve 111 is communicated with the chamber 110. The outlet of the control valve 111 is communicated with the suction chamber 106 via a passage 113. A solenoid 111a located in the control valve 111 is selectively excited and de-excited based on various parameters such as the temperature of the passenger compartment. The control valve 111 opens and closes a passage between the crank chamber 100 and the suction chamber 106 by exciting and de-exciting the solenoid 111a. In other words, the control valve 111 controls the amount of refrigerant gas flow from the crank chamber 111 into the suction chamber 106 in accordance with the temperature of the passenger compartment, thereby controlling the pressure in the crank chamber 100. Change in the crank chamber's pressure changes the difference between the pressure in the crank chamber 100 and the pressure in the suction chamber 106. Accordingly the inclination angle of the wobble plate 101 is changed. The change in the wobble plate's inclination angle changes the stroke of each piston 104. The displacement of the compressor is thus controlled.
In the above compressor, the electromagnetic control valve 111 is accommodated in an accommodating hole 114 defined in the rear housing 112. The accommodating hole 114 needs to be formed by cutting the rear housing inwardly from its surface. Accurately machining the hole 114 is extremely troublesome.
In addition, the structure of the control valve 111 varies depending upon the usage pattern of the compressor. This means that the hole 114 must be machined to fit the size and shape of the individual control valve 111 of various type. Machining of the hole 114 thus cannot be standardized. This complicates mass production of compressors having the hole 114. Further, different types of rear housings 112 having different structures are required in the assemblage of a compressor. This results in a high manufacturing cost.
An objective of the present invention is to provide a variable displacement compressor that is easy to manufacture.
Another objective of the present invention is to provide a variable displacement compressor that is suitable for mass production.
Yet another objective of the present invention is to provide a variable displacement compressor that can be manufactured for a reasonable cost.